(1) Field of the Invention
The present invention relates to a crane control method, and more particularly to a method of controlling a crane which makes it possible during transverse travel of the trolley to precisely transport parcels to the aimed location without substantial swing motions of the rope for suspending the parcels.
(2) Description of the Prior Art
To properly operate a crane, such as a container crane, in facilities in a port, for example, skill is required to exactly unload at the aimed point while restraining the suspended parcels from swinging.
Prior art methods of controlling a crane are known which make the crane travel, constraining the swing of the suspended parcels.
One of the prior art methods is the one in which the swing angle of the rope suspending the parcels is measured and feedback is applied so as to reduce the swing. This method, however, is not practical, since it is difficult to measure the swing angle.
A second prior art method is the one in which the velocity of the trolley is made to follow an objective velocity pattern calculated beforehand so as to restrain the swing of the suspended parcels, as described in Laid-open Japanese Patent Application No. 95094/83 or in U.S. Pat. No. 3,921,818. According to this method, the tractive force must have a margin so as to be able to correct the difference between the actual and objective speeds of the trolley due to external disturbances, such as wind. Furthermore, it is impossible to utilize the capability of the driving motor to the maximum extent in order to make the trolley travel to the optimum point in the minimal time and, as a result, there is a problem in that the cycle time is rather long.